Friction-welded shaft-disc assembly and method for the manufacture thereof

ABSTRACT

A composite shaft/disc workpiece which is assembled from a disc with a passage hole and from a shaft by friction welding is disclosed. The outer wall of the shaft has a plurality of steps in the connection region with the disc, the radius of the steps becoming larger in a direction of the axis. The passage hole of the disc is provided with webs, the radius of which likewise becomes larger in a direction of the axis and between which annular recesses are present. The webs and steps to be connected overlap in the radial direction, so that, during the welding of the shaft and disc, annular connecting portions are obtained in the region of the webs and steps, annular cavities being formed between the connecting portions. The cavities represent a weight saving, as compared with composite shaft/disc workpices made of solid material, and can also be used as parts of media ducts.

BACKGROUND AND SUMMARY OF THE INVENTION

This application claims the priority of German Patent Document 199 34855.3, filed Jul. 24, 1999, and PCT/EP00/05587, filed Jun. 17, 2000, thedisclosures of which are expressly incorporated by reference herein.

The invention relates to a composite shaft/disc workpiece assembled byfriction welding and to a method for producing the same.

In vehicle and machine building, composite workpieces composed of ashaft and of an essentially rotationally symmetrical disc are employedin numerous applications. Examples of such discs are gear and clutchparts or else disc-shaped blanks which still have to be machinedmechanically.

European Patent Document EP 372 663 A1 discloses a method, with the aidof which a shaft and a disc can be connected in a connection region bymeans of friction welding. For this purpose, the shaft is provided inthe connection region with a conical or stepped outer surface, while thedisc is provided with a conical or stepped passage hole corresponding tothe connection region on the shaft. This configuration of the connectionregion has the effect of centering the shaft in relation to the discduring the friction-welding operation. When the shaft is being welded tothe disc, either two conical individual surfaces of approximatelynegative shape meet one another, so that the friction-welded componenthas a coherent conical connection surface, or a plurality of radiallyadjacent planar annular surfaces offset in the axial direction meet oneanother, so that a connection surface composed of a plurality of planarsteps is obtained. In both cases, a large-area connection region whichis approximately free of cavities is obtained.

With a view to saving weight in engines, transmissions, etc., it isadvantageous to use composite shaft/disc workpieces, the shafts of whichare designed as hollow shafts. The method described in EP 372 663 A1, inwhich the steps or the cone in the connection region serve(s) forcentring the shaft in relation to the disc and in which a large-areaconnection region between the shaft and the disc is obtained, cannot beemployed, however, particularly in the case of thin-walled hollowshafts, since the wall of the hollow shaft is softened as a result ofthe large-area heating during friction welding, to an extent such that,when the disc is pressed on, deformation of the shaft wall is initiated.In the method of EP 372 663 A1, therefore, the hollow shaft cannotoppose the disc in the connection region with sufficient pressureresistance for welding, and the disc can be slipped over the connectionregion, instead of making a fixed rigid connection with the hollowshaft.

Furthermore, particularly in the case of shafts rotating at high speed,for example in transmissions, it is necessary to achieve a furthersaving of weight and a low mass moment of inertia in relation to theaxis. There is therefore a great need for composite shaft/discworkpieces which have a reduced weight, in particular, even in regionsdistant from the axis, that is to say even in the region of the disc,and at the same time a high design strength of the shaft/disc connectionmust be ensured.

The present invention provides a composite shaft/disc workpiece whichhas a reduced weight, as compared with the prior art, and has a low massmoment of inertia in relation to the axis of rotation. Further, a methodfor producing such a composite workpiece is provided.

Accordingly, the shaft is provided, in a connection region in which thedisc is to be welded to the shaft, with a plurality of rotationallysymmetrical steps, the diameter of which becomes increasingly large in adirection of the axis. On the other hand, the disc is provided with apassage hole in the region of the axis of rotation. The passage hole isconfigured in such a way that it has a plurality of rotationallysymmetrical webs which project from the disc towards the axis ofrotation. The inside diameter of the webs is selected such that each webforms a passage hole, the inside diameter of which is smaller by awelding overlap than the step which is located in the connection regionof the shaft and which is opposite this web in the assembled position.The disc is assembled, together with the shaft, by friction welding. Atthe same time, the webs are connected to the steps, and, in the regionof the webs, annular weld seams are obtained which, depending on thesize of the welding overlap, have a more or less conical shape. Annularcavities are obtained at the same time between successive webs.

Considerable weight savings can be achieved by means of these cavities,as compared with a conventional filled connection region. In particular,the mass moment of inertia of the composite workpiece composed of theshaft and the disc can thereby be greatly reduced. A high rigidity ofthe connection is achieved by means of the annular weld seams which lieparallel to one another. Good welding quality is ensured when thewelding overlap of the webs in relation to the steps is about 1 mm to 3mm. The weld seams formed in this case cover a region of 5 mm to 15 mmin the axial direction of the composite workpiece and are slightlytilted conically in relation to the axial direction of the compositeworkpiece.

In order to achieve the greatest possible saving of weight of thecomposite workpiece composed of the shaft and disc, it is advantageousto design the shaft as a hollow shaft. In order to avoid a radialbulging of the hollow shaft in the direction of the axis during frictionwelding, particularly when a hollow shaft of small wall thickness isused, the interior of the hollow shaft is provided in the connectionregion with a supporting element, by means of which deformations of thehollow shaft are prevented.

A particularly large saving of weight and reduction in the mass momentof inertia is achieved when the disc is composed of a conicalsheet-metal dish and of a supporting frame, the supporting frame havinga plurality of annular supporting webs, to which the sheet-metal dish isfastened. The supporting webs give the sheet-metal dish rigidity, whilethe weight of the disc is reduced by means of the cavities locatedbetween the supporting webs. The sheet-metal dish and the supportingstructure may in this case consist of different materials. Thus, thesheet-metal dish may be manufactured from a carbon steel which iscapable of tolerating the highest possible compressive and frictionalforces, while the supporting structure is produced from a suitablelightweight material. The webs of the supporting frame are expedientlyconnected by friction welding to the sheet-metal dish wall locatedopposite them.

The cavities formed between the webs and the outer wall of the shaft inthe assembled position may expediently be used for carrying liquid andgaseous media. In particular, they serve for the radial (circulatory)distribution of lubricating oil or pressure oil which is carried via oilducts inside the shaft and is guided onto the outer surface of the shaftat defined locations in the surroundings of the disc. The annular cavityin this case makes it possible to have a substantial simplification inthe geometry and production of the oil ducts. Arranging the bores inpairs opposite one another reduces unbalance.

The method according to the invention makes it possible to connectshafts to discs made of different materials. In particular, it allows areliable assembly of a disc consisting of any desired friction-weldablematerial together with a hardened steel shaft. The disc and shaft canthus be ready-machined separately and hardened, as required, before theyare assembled to form a composite workpiece.

The invention is explained in more detail below by several exemplaryembodiments illustrated in the drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1a shows a view of a disc and of a shaft which are to be assembledto form a composite shaft/disc workpiece.

FIG. 1b shows a view of the friction-welded composite shaft/discworkpiece.

FIG. 1c shows a view of the friction-welded composite shaft/discworkpiece, rotated through 90 degrees about the shaft axis in relationto FIG. 1b.

FIG. 1d shows, as a detail, a view of the region Id marked in FIG. 1b.

FIG. 2a shows a view of a composite workpiece consisting of a disc andof a hollow-shaft wall supported in the welding region by a ball.

FIG. 2b shows, as a detail, a view of a composite workpiece consistingof a disc and of a hollow shaft supported in the welding region by acylindrical piece, according to the inset IIb marked in FIG. 2a.

FIG. 3 shows a view of a composite workpiece consisting of a disc and ofa hollow shaft with a rotating shaft inside the composite workpiece.

FIG. 4 shows a view of a composite shaft/disc workpiece with a builtdisc.

DETAILED DESCRIPTION OF THE DRAWINGS

FIG. 1a shows a rotationally symmetrical disc 1 with a passage hole 2and a shaft 3, which are to be assembled together to form a compositeshaft/disc workpiece 4 illustrated in FIGS. 1b and 1 c. The disc 1 has,in the region of the passage hole 2, two annular webs 5, 5′ which facethe shaft 3 and enclose an annular recess 6. The shaft 3 has, in aconnection region 7, two steps 8, 8′ which, when the shaft 3 and disc 1are assembled, are connected to the webs 5, 5′ of the disc 1 in such away that the step 8 coincides with the web 5 and the step 8′ with theweb 5′.

The inside diameter 9 of the web 5 is smaller by a welding overlap 10than the outside diameter 11 of the step 8, and the inside diameter 9′of the web 5′ is smaller by a welding overlap 10′ than the outsidediameter of the step 8′, so that shaft 3 and disc 1 overlap radially inthe region of these webs 5, 5′ and steps 8, 8′ before assembly.

The disc 1 and shaft 3 are connected to one another by friction welding.In this case, for example, as indicated by the arrow in FIG. 1a, theshaft 3 is set in rotation and displaced axially in the direction of the(stationary) disc 1 until the steps 8, 8′ of the shaft 3 come intocontact with the webs 5, 5′ of the disc 1 and at the same time have theeffect of heating the webs 5, 5′ and the steps 8, 8′ locally in theregions of mutual contact. In this case, softening and deformation ofthe webs 5, 5′ and of the steps 8, 8′ takes place in the surroundings ofthe regions of mutual contact. This gives rise to an assembly zone 12which, as illustrated by hatching in the illustration of a detail inFIG. 1d, runs obliquely to the shaft axis. During the assembly of theshaft 3 together with the disc 1, a fixed leak-tight connection of thewebs 5, 5′ to the steps 8, 8′ is obtained, so that the recess 6 betweenthe webs 5, 5′ forms a closed annular cavity 13 which is delimited, onthe one hand, by the recess 6 of the disc 1 and, on the other hand, bythe outer wall 14 of the shaft 3.

For applications in the engine and transmission sector, the shaft 3 anddisc 1 typically consist of steel materials. However, friction weldingalso makes it possible to assemble workpieces of different materialsand, in particular, also assemble hardened assembly points. Thus, theshaft 3 and disc 1 may consist of different materials or the shaft 3 maybe hardened in the connection region 7 even before assembly.

FIGS. 1b and 1 c show the welded composite shaft/disc workpiece 4, theview of FIG. 1c being rotated through 90 degrees about the shaft axis inrelation to the view of FIG. 1b . The shaft 3 is a solid shaft 15 which,for weight-saving reasons inter alia, is provided with two drilled innerspaces 16, 16′. Between the inner spaces 16, 16′ is located a separatingweb 17 which separates from one another and supports the two innerspaces 16, 16′. In the present embodiment, the inner space 16 located onthe right of the separating web 17 is connected to the outer wall 14 ofthe shaft 3 via an outlet orifice 18. The inner space 16′ located on theleft of the separating web 17 is connected via a connecting bore 19 tothe closed annular cavity 13 which is itself provided with an outletorifice 20 to the outer wall 14 of the shaft 3. The two inner spaces 16,16′ thus form parts of two independent media ducts 21, 21′ which overlapin the axial direction of the shaft 3 and in which, for example,pressure oil can be carried. Different pressures can be exerted viathese media ducts 21, 21′, at the outlet orifices 18, 20, on connectionelements (not illustrated in FIGS. 1b and 1 c) which are connectedfixedly or axially displaceably to the shaft 3. Instead of carryingpressure oil, the media ducts 21, 21′ may also be used for carrying ordistributing any other media, such as, for example, lubricating oil,compressed air, cooling media, etc., along the composite shaft/discworkpiece 4. Unbalances can be reduced by virtue of the symmetricalarrangement of the media ducts 21, 21′ with respect to the axis ofrotation.

As shown in FIG. 1a, the outlet orifices 18, 20 and the connecting bore19 may be introduced into the shaft 3 even before the shaft 3 and thedisc 1 are assembled. The friction welding of the steps 8, 8′ on theshaft 3 and of the webs 5, 5′ on the disc 1 gives rise, in theconnection region 7, to the annular cavity 13 which, together with theoutlet orifice 20, the connecting bore 19 and the inner space 16′, formsthe media duct 21′.

FIG. 2a shows a composite shaft/disc workpiece 4 which is built from ashaft 3 designed as a hollow shaft 22 and from a disc 1. To fasten thedisc 1 by means of friction welding, the outer wall 14 of the hollowshaft 22 is provided, in a similar way to the exemplary embodiment shownin FIG. 1a, with two steps 8, 8′, to which the webs 5, 5′ of the disc 1are connected. The steps 8, 8′ on the hollow shaft 22 may be produced bytransverse rolling, transverse extrusion or cutting machining of thehollow shaft 22.

For weight-saving reasons, it is often advantageous for the wallthickness selected for the hollow shaft 22 to be as small as possible.In this case, there is a particularly small wall thickness 23 of thehollow shaft 22 in the region of the step 8 having the smaller outsidediameter 11 (see, in this respect, FIG. 1a). To support this step 8, asupporting element 24 is positioned in the interior 25 of the hollowshaft 22 in such a way that the supporting element is located oppositethe step 8 and therefore that point on the hollow shaft 22 which is theweakest in terms of the friction-welding process. The supporting element24 prevents the hollow shaft 22 from bulging inwards in the region ofthe step 8 during friction welding and thus ensures that, even in thecase of thin-walled hollow shafts 22, the required frictional forces forwelding the steps 8, 8′ on the shaft 3 and the webs 5, 5′ on the disc 1can be applied.

FIG. 2a shows an exemplary embodiment, in which the supporting element24 is designed as a ball 26 which is pressed, before friction welding,into that region 27 of the interior 25 of the hollow shaft 22 which islocated opposite the step 8. The outside diameter 28 of the ball 26 isin this case adapted to the inside diameter 29 of the hollow shaft 22.During the friction welding of the web 5 together with the step 8, theplastic deformation of the relatively thin-walled hollow shaft 8 givesrise, in the surroundings of the pressed-in ball 26, to annular beads 30which have the effect of a fixed leak-tight fit of the ball 26 in theinterior 25 of the hollow shaft 22 after the cooling of the compositeshaft/disc workpiece 4. The interior 25 of the hollow shaft 22 istherefore divided by the ball 26 into two separate inner regions 16 and16′. By means of drilled outlet orifices 18, the inner region 16′located on the left of the ball 26 is connected to the outer wall 14 ofthe hollow shaft 22 and thus forms a media duct 21 which may be used,for example, for supplying lubricating or pressure oil to bearings orcavities which the outer wall 14 of the hollow shaft 22 forms withcounterpieces (not illustrated in FIG. 2a) in the region of the outletorifices 18. The inner region 16 located on the right of the ball 26 isseparated by the ball 26 from the inner region 16′ located on the left.The annular cavity 13 constitutes part of a further media duct 21′ whichis connected by the outlet orifice 20 to that outer wall 14 of thehollow shaft 22 which is located on the right of the disc 1 and by theinlet orifice 31 on the disc 1 to that outer region 32 of the disc 1which is located on the left of the web 5. This media duct 21′ thus hasthe effect of bridging the disc 1 axially inside the compositeshaft/disc workpiece 4.

All the inlet and outlet orifices 18, 20, 31 required for producing themedia ducts 21, 21′ may be applied to the disc 1 or the shaft 3 beforewelding, without an exact meridional assignment of the disc 1 and shaft3 thereby needing to be adhered to during assembly. To be precise, sincethe cavity 13 has a radially symmetrical annular shape, it does notmatter at which meridional position the inlet orifice 31 on the disc 1is positioned in relation to the outlet orifice 20 on the shaft 3,since, irrespective of the mutual positioning of the shaft 3 and disc 1,a continuous media duct 21′ is always formed. During thefriction-welding operation, the outlet orifice 20 on the shaft 3 or theinlet orifice 31 on the disc 1 may be used for the delivery ofprotective gas, depending on whether the disc 1 is rotated in relationto the shaft 3 or vice versa.

In the detail, shown in FIG. 2b, of the composite shaft/disc workpiece4, the supporting element 24 is a cylindrical piece 33 which has anoutside diameter 34 adapted to the inside diameter 29 of the hollowshaft 22 and which is pressed before friction welding into that region27 of the interior 25 of the hollow shaft 22 which is located oppositethe step 8. In order to cover the entire friction-welding region in theregion of the step 8, the thickness of the cylindrical piece 33corresponds approximately to the thickness of the web 5, to be assembledtogether with the step 8, on the disc 1. The outer wall 35 of thecylindrical piece 33 is provided with a peripheral annular groove 36,into which hollow-shaft material penetrates as a result of the plasticdeformation of the hollow shaft 22 during the friction-welding processand ensures a firm fit of the cylindrical piece 33 in the interior 25 ofthe hollow shaft 22 after cooling. A further weight saving can beachieved if the cylindrical piece 33 is produced from a lightweightmaterial, for example aluminium.

FIG. 3 shows a further exemplary embodiment of a composite shaft/discworkpiece 4 consisting of a hollow shaft 22 and of a disc 1. Guidedthrough the interior 25 of the hollow shaft 22 is a rotating inner shaft37, the outside diameter of which is smaller than the inside diameter ofthe hollow shaft 22, so that the inner shaft 37 can rotate, free ofcontact, in relation to the hollow shaft 22. In a similar way to theembodiment of FIG. 1b, here too, the disc 1 has two webs 5, 5′, in theregion of which the disc 1 is connected to the steps 8, 8′ of the shaft3. Between the webs 5, 5′, the disc has an annular recess 6 which, afterthe welding of the shaft 3 and disc 1, forms an annular cavity 13between the disc 1 and the outer wall 14 of the hollow shaft 22. Thecomposite shaft/disc workpiece 4 has a media duct 21′ which isconfigured in a similar way to the exemplary embodiment of FIG. 2a andtherefore comprises the inlet orifice 31 on the disc 1, the annularcavity 13 and the outlet orifice 20 on the hollow shaft 3. If theinterior 25 of the hollow shaft 22 is not required for guiding an innershaft 37, the interior 25 may also be used as a further media duct 21,through which, for example, lubricating oil is carried or distributedalong the hollow shaft 22.

Finally, FIG. 4 shows a composite shaft/disc workpiece 4 consisting of ashaft 3 and of a disc 1, the disc 1′ illustrated here consisting of aconical sheet-metal dish 38 and of a supporting frame 39. The supportingframe 39 comprises a rotationally symmetrical disc-shaped dish 40, fromwhich a plurality of annular supporting webs 41 project approximately inthe axial direction and are connected by friction welding to the rearwall 42, located opposite them, of the sheet-metal dish 38. Thesupporting webs 41 give rise, between the rear wall 42 of thesheet-metal dish 38 and the dish 40 of the supporting frame 39, toannular cavities 43 which represent a considerable saving of weight anda reduction in the mass moment of inertia of the disc 1′ illustratedhere, as compared with the discs 1 made of solid material which areillustrated in FIGS. 1 to 3. For the composite shaft/disc workpiece 4 tobe used in a transmission, the sheet-metal dish 38 consists of ahigh-strength material which is insensitive to abrasive forces, forexample of a carbon steel. The supporting frame 39 having the supportingwebs 41, to which the sheet-metal dish 38 is fastened radiallyperipherally at different distances from the axis of rotation, preventsa deformation of the sheet-metal dish 38 under the high compressive andshearing forces acting on it. Since different materials can be connectedto one another by friction welding, the supporting frame 39 may bemanufactured from a lightweight material, for example aluminium, for afurther weight saving. The disc 1′ assembled in this way from thesheet-metal dish 38 and the supporting frame 39 has two annular webs 5,5′ in the region facing the axis of rotation of the shaft 3, one web 5being part of the supporting frame 39, while the other web 5′ is formedby the near-axis region of the sheet-metal dish 38. Between the two webs5, 5′ there is an annular recess 6. The shaft 3 is provided with twosteps 8, 8′, by means of which the webs 5, 5′ of the disc 1 areconnected by friction welding to the steps 8, 8′ of the shaft 3 in asimilar way to the exemplary embodiments described above, obliqueassembly zones 12 being formed.

While, in the exemplary embodiments shown, the connection between theshaft 3 and the disc 1 is formed by the connection of two webs 5, 5′ totwo steps 8, 8′, so that a single annular cavity 13 is obtained betweenthe webs 5, 5′ and steps 8, 8′, in general the shaft 3 and the disc 1may also have further web/step connections in the connection region 7.Further annular cavities 13 are thereby obtained, which are locatedbetween the disc 1 and the outer wall of the shaft 3.

What is claimed is:
 1. Composite shaft/disc workpiece comprising: ametallic shaft of circular cross section, an outer wall of which has aplurality of steps in a connection region, a diameter of the stepsbecoming larger in a direction of an axis; and an essentiallyrotationally symmetrical disc with, in a region of an axis of rotation,a passage hole which, in the assembled position of the disc and shaft,covers the connection region of the shaft in the axial direction, theshaft and disc being connected to one another by friction welding,wherein the passage hole of the disc has a plurality of rotationallysymmetrical webs, an inside diameter of which, before the welding of theshaft and disc, fall short by a welding overlap of an outside diameterof the steps located opposite them in the assembled position, andwherein the webs of the disc are connected to the steps of the shaft byfriction welding, with the result that an annular cavity is obtainedbetween two adjacent webs.
 2. Composite workpiece according to claim 1,wherein the welding overlap is between 1 mm and 6 mm.
 3. Compositeworkpiece according to claim 1, wherein the shaft is provided withoutlet orifices and/or connecting bores and/or the disc is provided withinlet orifices which issue into the annular cavity.
 4. Compositeworkpiece according to claim 1, wherein the disc consists of a conicalsheet-metal dish and of a supporting frame, the supporting frame havinga plurality of annular supporting webs which project approximately inthe axial direction and to which the sheet-metal dish is fastened. 5.Composite workpiece according to claim 4, wherein the sheet-metal dishand the supporting frame are connected by friction welding.
 6. Compositeworkpiece according to claim 4, wherein the sheet-metal dish and thesupporting structure consist of different materials.
 7. Compositeworkpiece according to claim 1, wherein the shaft is a hollow shaft. 8.Composite workpiece according to claim 7, wherein an interior of thehollow shaft is closed in the connection region by a supporting element.9. Composite workpiece according to claim 1, wherein the shaft consistsof steel and is hardened in the connection region.
 10. Method forproducing a composite shaft/disc workpiece consisting of a metallicshaft of circular cross section, an outer wall of which is provided, ina connection region located in a defined axial position, with aplurality of steps, a diameter of which becomes larger in a direction ofan axis, and of an essentially rotationally symmetrical disc with apassage hole in a region of an axis of rotation, the disc being fastenedto the shaft by friction welding, wherein the disc is provided, in theregion of the passage hole, with a plurality of rotationally symmetricalwebs, an inside diameter of which fall short by a welding overlap of anoutside diameter of the steps located opposite them in the connectionregion on the shaft, comprising the step of welding, at the same time asa deformation of the webs and of the steps located opposite them, tofasten the disc to the shaft in the defined axial position.
 11. Methodaccording to claim 10, wherein, before welding, the shaft and the discare provided with inlet and/or outlet orifices for media ducts, the saidorifices issuing into the outer wall of the shaft or of the disc.
 12. Amethod for producing a composite shaft/disc workpiece wherein the shaftincludes a plurality of steps and wherein the disc includes a pluralityof webs, comprising the steps of: disposing the disc on the shaft;mating the plurality of steps with the plurality of webs; and forming acavity by the mating of the plurality of steps with the plurality ofwebs on an outer circumference of the shaft.
 13. The method of claim 12,further comprising the step of deforming the steps and the webs whensaid steps and webs are mated.
 14. The method of claim 12, furthercomprising the step of friction welding the plurality of steps to theplurality of webs.
 15. The method of claim 12, further comprising thestep of disposing a supporting element within the shaft between opposingsteps.
 16. The method of claim 15, wherein the supporting element is asphere.